Methotrexate-Induced Folate Deficiency Anemia

Clinical Presentation and Diagnosis

The American Academy of Dermatology states that macrocytic anemia with elevated MCV is a hallmark finding of folate deficiency from methotrexate, which is consistent with this patient's presentation of macrocytic anemia with MCV 108 1, 2
Four months of unsupervised methotrexate use without folate supplementation is a critical risk factor for folate deficiency 1, 3
The British Journal of Dermatology notes that early bone marrow toxicity manifests as increased mean corpuscular volume, which is consistent with this patient's elevated MCV 2
Anemia of chronic disease is excluded because it is typically normocytic or microcytic, not macrocytic, and this patient has an elevated MCV of 108 1, 2

The British Journal of Dermatology recommends discontinuing methotrexate immediately until hematologic parameters normalize 2, 3, 4
The American Academy of Dermatology states that folate supplementation reduces hepatic abnormalities and GI adverse effects without compromising efficacy, and recommends mandatory folate supplementation with 1-5 mg daily when restarting methotrexate 1, 3, 5
The American Academy of Dermatology reports that pancytopenia can occur after even a single dose of methotrexate in patients with risk factors, and recommends monitoring CBC every 3-4 months after the first 1-2 months of therapy 1, 3, 5
The British Journal of Dermatology recommends withholding or decreasing methotrexate dose if MCV exceeds 105 fL 2

Folic acid supplementation at least 5 mg per week reduces gastrointestinal and liver toxicity without compromising methotrexate efficacy, as recommended by the Annals of the Rheumatic Diseases 6

The American Academy of Dermatology recommends initiating folinic acid (leucovorin) rescue therapy if there is concern for acute methotrexate toxicity, particularly if the patient has additional risk factors such as renal impairment or concurrent NSAID use, with leucovorin at 10 mg/m² administered immediately, and subsequent doses every 6 hours if severe toxicity is suspected 7
When restarting methotrexate, mandatory folate supplementation with 1-5 mg daily is essential, except on the day of methotrexate dosing, to prevent recurrence, as recommended by the Journal of the American Academy of Dermatology 7

The Annals of the Rheumatic Diseases is not cited, however, the Journal of the American Academy of Dermatology recommends at least 5 mg per week of folic acid supplementation to reduce gastrointestinal and liver toxicity without compromising methotrexate efficacy, although the exact dosage is not specified in this context 7